Method of resisting corrosion in metal reinforcing elements contained in concrete and related compounds and structures

ABSTRACT

In some embodiments, alternate sources of aluminum or calcium are provided in various ways including the desired compounds. The further object of the present invention contemplate in situ creation of the compound in interest in fresh concrete and as a slurry which can be employed in remediation of existing concrete structures. A method of resisting corrosion in concrete containing metal elements is provided. It includes introducing into fresh concrete, containing metal elements, at least one compound capable of sequestering chloride ions. The method may also involve employing a compound which is capable of establishing a corrosion resistant oxide layer on the metal reinforcing elements. The invention also includes certain compounds which may be employed in the method as well as concrete structures containing the compounds. In another embodiment of the invention, concrete structures may be rehabilitated by providing an overlay containing a compound of the type which will contribute to corrosion resistance either through chloride ion sequestering or creating barriers around metal structural elements with the overlay being provided in situ or as a preformed member and with possible use of a slurry in combination with an overlay segment. In another embodiment, a source of alumina is combined in solution with Ca(NO 2 ) 2  and/or NaNO 2  with the resultant solution being introduced into the pores of a concrete structure, preferably under pressure to cause them to react with each other and with Ca(OH) 2  contained within the concrete to produce the desired corrosion inhibiting compound.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Ser. No. 10/044,660entitled “A METHOD RESISTING CORROSION IN METAL REINFORCING ELEMENTSCONTAINED IN CONCRETE AND RELATED COMPOUNDS AND STRUCTURES” in the nameof Paul W. Brown filed on Jan. 9, 2002, which is a continuation-in-partof U.S. Ser. No. 10/010,581, filed Nov. 13, 2001 now U.S. Pat. No.6,610,138.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of introducing into freshconcrete, as herein defined, compounds capable of sequestering chlorideions to establish resistance to corrosion of metal reinforcing elementscontained within or contacting the concrete and provide a corrosionresistant oxide layer on the metal reinforcing elements, as well asrelated compositions and structures. The invention is also directedtoward corrosion protection of concrete articles wherein the concretehas already set and hardened.

2. Description of the Prior Art

The advantageous use of metal reinforcing members, such as steelreinforcing members, in concrete for structural uses has been known formany years. Concrete is known to provide desired compressive strength,but tends to lack tensile strength. The reinforcing bars co-act with theconcrete to provide enhanced tensile strength for the combination ofmaterials. It has also been known to employ corrugated metal deck incombination with concrete to create a composite with similar benefits.Numerous other metal members have been embedded in concrete or providedin contact therewith to achieve enhanced benefits in the structuralenvironment as a result of such materials. Among these additionalmaterials are grids, beams, bolts, hold-downs and wire mesh.

One problem with such construction has arisen as a result of exposure ofconcrete to salts, such as calcium chloride and sodium chloride, onexternal structural members to resist the undesired accumulation of snowand ice on bridges and other concrete paved areas such as roadways,parking lots, sidewalks and the like. While these chloride salts doprovide benefits in terms of de-icing of concrete surfaces, theyfrequently result in the chloride solutions migrating into the concretedecks and adjacent vertical concrete surfaces, such as walls andcolumns, also subjecting these to chloride intrusion. Also, salineseawater may migrate into the pores of concrete exposed to seawater asin sea walls, With respect to bridge decks, in particular, an enhancedproblem results from air movement under the deck creating an environmentwherein the salts are aspirated into the concrete and salt ladensolutions flow into the pores.

Regardless of the manner in which chloride enters such concrete, thechloride, upon reaching the steel reinforcing members, tends toaccelerate corrosion of the same because the oxidation of the metalmetallic iron to Fe²⁺ is catalyzed by the chloride. Also, oxides andhydroxides of Fe²⁺ frequently form and occupy porosity in the vicinityof the interface of the steel and concrete. In addition, oxides andhydroxides of Fe³⁺ may also be produced. As these iron oxides andhydroxides are of greater volume than the iron metal from which theywere produced, they tend to cause internal stresses which may becomehigh enough to crack the concrete, and also degrade the desired bondbetween the metal reinforcing elements and the concrete.

U.S. Pat. No. 5,049,412 discloses a method of re-alkalizing concrete inwhich carbonation has occurred. An outer layer of the concrete structurecontaining reinforcement which layer through exposure to air has beencarbonated has an adjacent layer that remains relatively lesscarbonated. The patent discloses applying to the outer surface a watertype adherent coating followed by introducing between the outer adjacentlayers, water from a source external to the concrete structure andmaintaining the concrete structure in this condition for a period oftime sufficient to effect diffusion of the alkaline materials from therelatively less carbonated adjacent layer into the relatively carbonatedouter layer.

U.S. Pat. No. 5,198,082 discloses a process for rehabilitation ofinternally reinforced concrete, which includes temporary application ofan adhered coating of an electrode material to surface areas of theconcrete. Distributed electrodes such as a wire grid is embedded in thecoating. A voltage as applied to the reinforcement and distributed tothe electrode to cause migration of chloride ions from the chloride intothe electrolytic coding. Among the shortcomings of this approach are theneed to provide, at the local source, a source of electrical power. Thiselectrical equipment might have to be maintained at the site forextended periods of time. This further complicates matters byestablishing a risk of injury to children and others that might find theequipment at an attractive nuisance, as well as the risk of theft andvandalism. Also, such chloride extraction processes may alter theconcrete microstructure by making it more porous and permeable, thereby,facilitating enhanced re-entry of chloride when de-icing salts are againapplied to the exterior.

It has been known to employ nitrites, such as calcium nitrite, inresisting corrosion of steel parts in concrete. It is believed that thenitrites oxidize the Fe²⁺ to Fe³⁺ which, in turn, precipitates as Fe₂O₃.The Fe₂O₃ thus formed tends to act as a barrier to further contactbetween the chloride and the steel. See, generally, U.S. Pat. Nos.4,092,109 and 4,285,733. Neither calcium nitrate nor Fe₂O₃, however,function to sequester chloride. The latter provides merely a barrier.

There remains, therefore, a very real and substantial need for a methodand related composition and structure which will resist undesiredcorrosion of metal structural elements contained within, or in contactwith, concrete structural members.

SUMMARY OF THE INVENTION

The present invention has met the above-described need.

The method, in one embodiment, includes resisting corrosion in concretecontaining metal reinforcing elements composed of steel, copper,galvanized steel, tin plated steel or other structurally suitable metalsby introducing into fresh concrete containing metal reinforcing elementsat least one compound capable of sequestering chloride ions in a lowsolubility compound.

In connection with steel reinforcing elements, a low solubility compoundwithin which the chloride ions are sequestered preferably also iscreated in a reaction that releases nitrite, which serves to oxidizeFe²⁺ to thereby provide a corrosion-resisting oxide layer on the steelreinforcing elements. This, therefore, in connection with steel achievestwo levels of corrosion resistance, one of which is the actual capturingor sequestering of the potentially damaging chloride ions, and thesecond of which provides a protective layer on the metal reinforcingelements.

Among the preferred compounds for use in the method of the presentinvention are one or more compounds selected from the group consistingof 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O; 3CaO.Al₂O₃.Ca(NO₃)₂.nH₂O; and3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O; wherein n=0 to 24 and preferably 10 to 24,depending upon the relative humidity to which a compound isequilibrated. If desired, lower values of “n” may be obtained by dryingat low relative humidity as by evacuation or by heating, for example.

A further compound employed in another embodiment of the invention is,3Me(II)O.R₂O₃.Me(II)(anion)₂.nH₂O wherein Me(II) is one or more divalentcations, such as Ca for example, R₂ is Al₂, Fe₂ or Cr₂ anion is NO₂,NO₃, CO₃, BO₄ or OH and n is 0 to 24, and preferably 10 to 24. For someformulations, the anion may be divalent. In this case the formula wouldbe Me(II)O.R₂O₃Me(II)(anion)nH₂O wherein n is 0 to 18 and preferably 10to 18.

The invention also contemplates a concrete structure which has hydratedfresh concrete and a plurality of metal structural elements in contactwith the hydrated fresh concrete with a compound which sequesterschloride ions dispersed within the concrete.

The invention in another embodiment contemplates rehabilitation ofexisting concrete structures by providing a chloride sequesteringcompound in a member adjacent to the concrete structure and having acomposition such that migration of chlorine ions away from metalstructural elements in the concrete structure and into the adjacentoverlay may be effected. In addition, if desired, release of nitrite tomigrate into the concrete structure and afford corrosion protection toembedded steel.

In one version, the overlay, which may be formed in situ or as apreformed panel, contains the chloride-sequestering compound. Inanother, a slurry may be applied to the concrete structure with orwithout an overlay secured thereover.

The invention also contemplates in situ formations of the desiredcompounds which are suitable for either chloride ion sequestration andnitrite release in order to establish an oxide protective layer over themetal elements.

The compound may be formed by adding certain materials to fresh concretewith a reaction product of cement hydration yielding a further componentor separately adding the component. The in situ concept may also beemployed in remediation of existing concrete structures.

Alternate sources of aluminum for use in creating the compound may beprovided.

In another approach, sources of calcium and aluminum may be providedseparately or as an admixture introducing the desired compound.

It is an object of the present invention to provide a method and relatedcompounds and structures for inhibiting corrosion of metal elementspositioned within or in contact with concrete in a structuralenvironment.

It is a further object of the present invention to provide such a systemwherein undesired chloride ions will, as a result of a reaction, besequestered, thereby reducing their ability to corrode the metalelements.

It is yet another object of the invention to, through a reactioneffecting such sequestration of ions, to provide free nitrites whichwill oxidize the Fe2+to a Fe³+ion which, in turn, precipitates as Fe₂O₃which coats the metal element and, thereby, resists corrosion.

It is yet another object of the present invention to provide such asystem which employs unique compounds.

It is another object of the present invention to provide such a systemwhich will effectively and rapidly provide corrosion resistance to steeland other metals.

It is yet another object of the invention to provide such a system whichmay be employed by merely adding one or more compounds of choice tofresh concrete without requiring substantial changes in conventionalpractices employed in producing and placing the concrete structure.

It is a further object of the present invention to provide such a systemwhere an existing concrete structure may be rehabilitated through bysequestering the chloride and providing a means to accumulate nitriteions in the vicinity of the embedded steel. It is appreciated that thenitrite ions oxidize presently corroding steel to produce a protectivelayer. In some formulations nitrite ions may not be available and inthese instances rehabilitation is the result of chloride sequestrationonly.

It is yet another object of the present invention to provide such asystem wherein an overlay, which contains a composition which may be ofthe type employed in other embodiments of the invention and facilitatessequestering of chloride and corrosion protection of metal structuralelements. In another version, a slurry containing the compound ofinterest may be applied to the concrete structure with an overlaymaterial either formed in situ or as a preformed panel securedthereover.

It is yet another object of the present invention to provide such asystem for rehabilitation of existing concrete structures withoutrequiring a source of electrical energy to be present on an ongoingbasis during the performance of the method.

It is a further object of the present invention to provide for creationof the desired compound in situ in fresh concrete, or as a component, orwith it, employed with one or more components employed in creating thefresh concrete.

It is yet another object of the present invention to provide in situcreation of the desired compound in the course of creating a slurry orpreformed panel employed in remediation existing concrete structures.

It is yet another object of the present invention to provide for such insitu creation of the compound by adding certain materials either insolution or in the mixing water employed to prepare the concrete.

It is yet another object of the present invention to employ sources ofaluminum other than calcium aluminate cement in creating the desiredcompound.

It is further an object of the present invention to provide alternatesources of calcium and aluminum in creating the desired compound.

These and other objects of the invention will be more fully understoodfrom the following description of the invention with reference to thedrawings appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional illustration of a concrete bridgedeck containing metal reinforcing elements.

FIG. 2 is a schematic cross-sectional illustration similar to FIG. 1,but showing a construction having an overlay containing the chloridesequestering composition.

FIG. 3 is a schematic cross-sectional illustration similar to FIG. 2except that the overlay consists of a slurry adjacent to the concretestructure and an overlaying material.

FIG. 4 illustrates a cross-sectional illustration looking downward on aconcrete piling which is to be rehabilitated through the system of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As employed herein the term “concrete structure” refers to an existingstructure which is composed in at least significant part of concretewhich has set and hardened, as contrasted with “fresh concrete” asdefined herein and shall expressly include, but not be limited to,bridges, roadways, parking lots, sidewalks, parking garages, floors,support columns, piers, marine structures, piling, conduits and otherconcrete structures whether located inside or outside, and whethersubject to vehicular or foot traffic thereover or not.

As employed herein, the term “fresh concrete” means concrete which is ina plastic state.

As employed herein reference to “introducing” a compound into freshconcrete shall be deemed to include introducing the compound in solidform and in slurry form with or without other ingredients such asminerals and additives into fresh concrete and shall also embraceadmixing or blending the composition in dry form with dry cement and/orother ingredients prior to water being added.

As employed herein, the term “metal elements” means metal elementsplaced within or in contact with concrete for various purposesincluding, but not limited to, structural purposes and shall expresslyinclude, but not be limited to, reinforcing bars, grills, beams, metaldeck hold downs and wire mesh.

As shown schematically in FIG. 1, a layer of concrete 2, overlies and issupported by a deck member 4. The concrete in the form shown has aplurality of elongated, generally parallel, reinforcing bars 6, 8, 10,12, 14, 16, 18. This assembly may be created in a conventional manner toprovide the desired structure which, in the form shown, may be a bridgedeck having an undersurface 22, exposed to air 24 and an upper surface26, which may have undesired snow deposited thereon or ice formedthereon. Application of calcium chloride, sodium chloride or otherchloride containing salts to the upper surface 26, or the overlying iceand snow (not shown) results in chloride penetration into the concreteinterior and, if not inhibited, contact with the metal reinforcing bar6-18 (even numbers only) which will generally be composed of steel tocreate the undesired corrosion.

For convenience of reference herein, the use of metal elements such assteel reinforcing bars 6-18 (even numbers only) will be discussed. Itwill be appreciated that corrosion inhibition of other types of metalelements such as those made of or coated with copper, tin or zinc, forexample, may benefit from the present invention.

In one embodiment of the invention, there is not only provided freenitrite, which oxidizes ferrous (Fe²⁺) to ferric (Fe³⁺) ion to therebyeffect precipitation of Fe₂O₃ to form an iron oxide barrier, but alsoprovides means to sequester chloride which enters the concrete porosityby capturing the same in low solubility compounds.

As employed herein the term “low-solubility compounds” means,chloride-containing compounds exhibiting solubilities substantiallybelow those of sodium chloride or calcium chloride, and shall include,but not be limited to, chloride-containing compounds, which atsaturation in aqueous solutions permit less than about 1 kg of solublechloride per cubic meter of concrete. A chloride level of about 1 kg/m³is considered the threshold level for corrosion.

In general, the invention contemplates the addition of any compound intowhich chloride ions would enter to produce a low solubility compoundthat sequesters the chloride.

An example of a preferred reaction of the present invention, whichaccomplishes both the objective of creating an iron oxide barrier andthe sequestering of chloride, is shown in reaction (1).

3CaO.Al₂O₃.Ca(NO₂)₂ .nH₂O+2Cl⁻→3CaO.Al₂O₃.C aCl₂ .nH₂O+2NO₂ ⁻.  (1)

In this example 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O wherein n=10 is added to freshconcrete as a particulate solid. The reaction that occurs is thechloride from the de-icing salts used on the hardened concrete reacts toproduce Friedel's salt, which sequesters the chloride and, in addition,serves to release nitrite in order to oxidize any Fe²⁺. In adding theparticulate compound, 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O, is added to the freshconcrete, it is preferred that in general about 3 to 88 pounds of theparticulate solid will be added per cubic yard of hydrated freshconcrete, and preferably about 22 to 66 pounds per cubic yard. The exactamount will be influenced by the anticipated rates of chloride ingressinto the concrete having the usual range of water-to-cement ratios,e.g., 0.35 to 0.50. The admixture may, if desired, be employed inconcrete having lower water-to-cement ratios such as 0.25 to 0.35, forexample, or higher ratios such as 0.5 to 0.9, for example. In general,the higher the anticipated rate of chloride ingress, the larger theamount of particulate composition employed. The compound is admixed withthe hydrated fresh concrete to achieve substantially uniformdistribution thereof. When the concrete sets, this constituent will bepresent in the concrete to receive and interact with chlorine from theicing salts that penetrates the pores of the concrete. This compound(3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O) is generally stable over the range of pHvalues normally encountered in concrete. The resultant compound3CaO.Al₂O₃.CaCl₂.1OH₂O is a low solubility compound within which thechloride is sequestered. This compound, is more stable than the nitrite.Chloride will exchange for the nitrite thereby freeing the nitrite andsequestering the chloride. As a result, the concentration of chloride inthe concrete at the surface of the steel, such as re-bars 6-18 (evennumbers only) will be reduced as compared with concrete not containingthe compound. This same reaction may be employed with the same resultsubstituting Fe₂O₃ for Al₂O₃ in the starting material. This would resultin the reaction 3CaO.Fe₂O₃.Ca(NO₂).nH₂O+2Cl⁻→3CaO.Fe₂O₃.CaCl₂.nH₂O+2NO₂⁻

In lieu of providing the compound such as 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O indry particulate form, it may be presented as a slurry with a pH of about10 or greater with the particulate being present in the slurry in therange of about 5 to 60 weight percent and preferably about 10 to 35weight percent. The slurry then would be admixed with the hydrated freshconcrete.

In lieu of introducing the particulate solid or slurry into hydratedfresh concrete, if desired, one may admix the particulate solid orslurry with one or more of the dry components of the concrete such asthe cement, for example.

In lieu of the compound employed in reaction (1), other compounds may beused to create essentially the same reaction with the followingdifferences. Among these compounds are, 3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O whereinn=0 to 24; 3CaO.Al₂O₃.Ca(NO₃)₂.nH₂O wherein n=0 to 24; and3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O wherein n=0 to 24.

Also, 3Me(II)O.R₂O₃.Me(II)(anion)₂.nH₂O wherein Me(II) is one or morecations, R₂ is Al₂, Fe₂ or Cr₂, anion is NO₂, NO₃ or OH and n=0 to 24may be employed. These approaches, in many instances, involve asubstitution in the compound employed in equation (1) for the aluminum,for the calcium or the nitrite. As to the substitution for the nitrite,this would be replaced by nitrate in equation (1)3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O or (3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O. As statedhereinbefore, the anion may be divalent in which case the formula wouldbe 3Me(II)O.R₂O₃.Me(II)(anion)nH₂O wherein n is 0 to 18 and preferably10 to 18. In other compositions, nitrite could be replaced by carbonate,borate or other anions.

The nitrites have the advantage of sequestering chloride in addition toliberating a species capable of rapidly oxidizing ferrous (Fe²⁺) ionsnear the surface of corroding seal to ferric (Fe³⁺) ions to facilitatethe formation of a protective layer of ferric oxide or hydroxide on thesteel.

It is understood that the value of “n”, meaning the number of waters ofhydration, may vary, depending on the relative humidity to which thecompounds are exposed.

Among the preferred compounds for use in the invention are,3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O and 3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O in terms ofeffectiveness for both chloride sequestration in concrete and protectiveoxide layer formation of metal embedded or in contact with concrete. Itis preferred that n=0 to 24.

EXAMPLE 1

In order to provide more detailed information regarding the manner ofsynthesizing the compounds, examples will be provided.

In the synthesis of 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O wherein n=0 to 24, thefollowing procedure may be followed.

In employing 3CaO.Al₂O₃ the following process of synthesis may beemployed:

In employing CaO.Al₂O₃ the following process of synthesis may beemployed:

The presence NaOH does not appear to interfere with sequestration ofchloride or with the action of nitrite on steel and, as a result, it isnot necessary to remove the NaOH by washing the product compounds.Alternatively, the 3CaO.Al₂O₃ and Ca(NO₂)₂.nH₂O can be crystallized andseparated from the NaOH solution.

In each of these two examples, the Ca(OH)₂ and calcium aluminate wereemployed as fine powders. Ca(NO₂)₂ and NaNO₂ are commercially availableand highly soluble in water. While there are no critical particle sizedistributions, in general, it is preferred to have a particle size suchthat 99% of the powder passes through a 325 mesh sieve. Commerciallyavailable Ca(OH)₂ was employed as was commercially available CaO.Al₂O₃with the latter being employed as a refractory cement. The synthesis ineach case was carried out at room temperature by mixing the reactiveswith approximately 10 times their weight of water in suitable sealedcontainers. Their reaction occurred more rapidly if the contents of thecontainers were stirred or agitated. Optionally, if desired, grindingmedia such as Zirconia media, for example, may be placed in thecontainers.

The nitrate chloride sequestering compound 3CaO.Al₂O₃.Ca(NO₃)₂.nH₂Owherein n=0 to 24 can be produced in the manner described in theforegoing two examples employing tri-calcium aluminate or mono calciumaluminate and calcium hydroxide.

In using 3CaO.Al₂O₃ as a starting material, the following process can beemployed.

wherein n=0 to 24.

Employing CaO.Al₂O₃ as the starting material, the following process canbe employed.

The presence NaOH does not appear to interfere with sequestration ofchloride or with the action of nitrite on steel and, as a result, it isnot necessary to remove the NaOH by washing the product compounds.Alternatively, the 3CaO.Al₂O₃.Ca(NO₃)₂.nH₂O and Ca(NO₃)₂ can becrystallized from the NaOH solution.

EXAMPLE 2

The phase 3CaO.Fe₂O₃.CaCl₂.nH₂O wherein n=10 has been created byreacting the precursors 3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O and3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O with chloride. This indicates that chlorideions can be sequestered in the Fe analog of Friedel's salt(3CaO.Al₂O₃.CaCl₂.10H₂O). The compounds 3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O and3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O have also been produced employing 2CaO.Fe₂O₃.in the presence of supplementary Ca from Ca(OH)₂ and nitrite or nitratefrom their calcium and/or sodium salts. 2CaO.Fe₂O₃ may be produced byblending Fe₂O₃ and CaCO₃ in a molar ratio of about 2:1 followed bysintering this mixture at 1150° C. for approximately 1.5 hours. Themixture of CaO and 2CaO.Fe₂O₃ is produced by calcining 3 moles of CaCO₃with 1 mole of Fe₂O₃ at 1100° C. for approximately 1.5 hours. A varietyof reaction times and temperatures can be used in the synthesis of thiscompound or this mixture. After cooling the 2CaO.Fe₂O₃ or the mixture of2CaO.Fe₂O₃ and CaO were ground to an average particle size ofapproximately 10 microns using known comminution techniques.

EXAMPLE 3

The compounds 3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O may be produced by calcining 1mole of CaCO₃ with 3 moles of Fe₂O₃ at 1100° C. for about 1.5 hours.This produces a mixture of CaO and 2CaO.Fe₂O₃. This mixture is thenground and reacted with either NaNO₃ or Ca(NO₃)₂ under basic conditions.In the event that NaNO₃ is used, it is preferred to add supplementalcalcium. This may be added as CaO or Ca(OH)₂ for example.

With respect to compound 3Me(II)O.R₂O₃Me(II)(anion)₂.nH₂O wherein R₂ isAl₂, Fe₂ or Cr₂ anion is NO₂, NO₃ or OH and n is 0 to 24 where Me(II) isa cation such as Ca, but may be partially substituted by other divalentcations or may be completely substituted by other divalent cations suchas Ba, Sr, Mn, Zn, for example. For some compositions divalent anionssuch as carbonate or borate may be used.

Referring to FIG. 2, wherein an existing concrete structure 2 havingreinforcing metal elements 6-18 (even numbers only) is shown with anunderlying deck member 4, which may or may not be present in connectionwith the rehabilitation of existing concrete structures as provided inthis embodiment of the invention. An overlay 30, which in the formillustrated, it is concrete containing a compound usable in the presentinvention to sequester chloride ions with or without the capability ofreleasing nitrites to establish an oxide coating on the metalreinforcing member 6-18 is shown. This overlay 30 preferably has aporosity similar, or in excess of, to that of the concrete in thestructure so as to permit free movement of chloride ions and nitritestherebetween. The thickness T of the overlay 30 may be in the order of0.5 to 10 inches with a preferred thickness being about 1-4 inches.

The overlay 30 may be established in situ and self-bonded to the uppersurface 32 of the concrete structure. In the alternative, the overlay 30may be a preformed panel containing the compound which may be secured tothe concrete structure 2 by any desired means such as an adhesivematerial preferably provide a continuously between the overlay 30 andthe concrete layer 2 without interfering meaningfully with porosity inthe interchange between the two structural elements or may be providedin certain locations leaving other areas for surface-to-surface contactbetween the overlay 30 and the concrete member 2. A suitable adhesivefor this purpose is latex.

In lieu of the concrete material employed in overlay 30, other suitablematerials having the desired strength, porosity and othercharacteristics needed for the present invention, may be employed. Amongthese are asphaltic materials, clay and clay-like materials and othercement materials including but not limited to Portland cements, blendsof Portland cement with other materials such as fly-ash, slag or silicafume, calcium aluminate cements and mortars.

The overlay 30 provides a number of beneficial actions, which facilitaterehabilitation of the existing concrete structure 2. First of all,chloride will migrate out of the concrete 2 in response to theconcentration gradient produced in the pore structure of the concrete 2,the pore structure across the interface with the overlay 30 and with thepore structure of the overlay 30 itself. The admixture in the overlay 30sequestered chloride ions that enter the overlay 30. Nitrite willmigrate from the overlay 30 into the concrete 2 and toward thereinforcing steel 6-18 (even numbers only) in response to theconcentration ingredient produced in the pore structure of the concreteitself, in the pore structure across the interface at surface 32 betweenthe concrete 2 and overlay 30 and within the pore structure of theoverlay 30 itself. The nitrite facilitates formation of a protectivecoating on the metal reinforcing elements 6-18, which may be composed ofsteel. All of this is accomplished without requiring prior art externalelectric current application. The system, therefore, results in passivechloride extraction.

If desired, in order to enhance the efficiency of maintaining thedesired continuous moisture path, through which the chloride ions andnitrite can move, additional wetting may be applied and a low porosityoverlay (not shown) overlying the upper surface 33 of the overlay 30 maybe provided in order to seal the moisture in the structure. Also, rainmay enhance such moisture paths. The low porosity overlay may be appliedas a self-bonding coating established in situ or as a preformed elementsecured to surface 33.

In employing the process in connection with FIG. 2 and the embodimentdescribing in connection with FIG. 3, the compounds previously disclosedherein may be employed. It will be understood that those compounds whichboth sequester chloride ions and release nitrite will result in both thesequestration of chloride ion and releasing of nitrite serving to createthe protective oxide layer around the metal reinforcing members 6-18 inthe manner described herein.

Referring to FIG. 3, there is shown an embodiment similar to that ofFIG. 2 except that the overlay 30 has a lower portion which is aseparately formed slurry 34 disposed between the upper surface 32 ofexisting concrete structure 2 and the upper portion of overlay 30 withthe overall thickness of the overlay 30 remaining within the range ofthickness T. The slurry will be porous to facilitate migration ofchloride ions and nitrite between it and the underlying concretestructure 2. The porosity of the slurry 34 will be such as to maintaincommunication with the underlying concrete 2. The slurry 34, which maybe employed alone (not shown) or in combination with another portion ofoverlay 30 as shown in FIG. 3, will contain the compound employed toeffect the objectives of the invention and may also include cements andsand as desired. In cases where slurry 34 is employed preferably aloneit has a thickness of about ⅛ inch to 4 inches. In general, the water tosolids ratio of the slurry will facilitate its being pumpable orspreadable with the capability of hardening with the consumption of freewater during formation of 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O, wherein n=0 to 24.The water to solids ratios may be about 0.25-5 and preferably about 0.4to 1.0. The slurry is pumped, sprayed, troweled or otherwise placed onthe surface 32 to create slurry layer 34. The thickness of the slurrypreferably will be in the range of about 0.125 to 4 inches and if sandis not present in the composition, will preferably be in the range ofabout 0.25 to 0.5 inch. With sand, the range is preferably about 0.5 to1.0 inch. It will be appreciated that if in lieu of the compositionpreviously recited in this paragraph, the composition3CaO.Al₂O₃.Ca(NO₃)₂.nH₂O, wherein n=0 to 24 were employed as nitrate isnot regarded as a corrosion inhibitor in the sense of creating an oxideprotective coating on the metal elements, this compound would providesolely a means for removing chloride ions from the concrete, but notinhibition of corrosion of embedded steel or other metal. The amount ofthe compound employed in a specific installation can be determined bythe amount of chloride that has entered the concrete structure and canbe determined readily by those skilled in the art.

Referring to an embodiment wherein the vertical concrete structural beremediated, FIG. 4 shows a piling 40 which is generally verticallyoriented and may be located under water. It has a plurality of elongatedsteel reinforcing members 42, 44, 46, 48, 50 embedded therein. Acontinuous clamshell 60 has been placed around the piling 40 to createan annular region 64 within which a slurry of the present invention maybe introduced. The clamshell 60 may be in segments which arelongitudinally adjacent to each other and secured to each other. Theymay be joined by bolts or other suitable mechanical means such ascables, or clamps. The annular region 64 has the slurry introduced afterthe clamshell 60 is placed in the space with the slurry being pumped into displace water within an annular region 64. In other respects, thesystem of the invention performs in the identical manner as previouslydescribed herein.

It will be appreciated that depending upon the specific nature of theconcrete structure to be remediated and the location and nature of theenvironment in which it is being employed, certain preferred refinementsof this embodiment of the invention may be employed. For example, insituations where vehicular or foot traffic may be imposed on theconcrete structure and an overlay with high strength should to beprovided. Also, for example, in situations were the concrete structurewill be subjected to a freeze-thaw cycles certain preferred approachesmay serve to minimize the effects of the same. For example, anair-entrained admixture may be provided in slurry 34 of FIG. 3 tocounteract the effects of the freeze-thaw cycles. Such an approach mightinvolve adding a chemical in a small amount, such as about 0.1% of theweight of the concrete, for example, to produce small bubbles when theconcrete freezes the water in the porosity migrates into the bubbles andfreezes harmlessly.

An alternate way of minimizing the effect of the freeze-thaw cycle wouldbe maintain a high ionic strength liquid in the porosity of the slurry.The more ions dissolved in water the lower the freezing temperature. Forexample, soluble nitrite salts such as calcium nitrite, calcium nitrite,sodium nitrate, or sodium nitrite may be employed for this purpose andfunction to increase the concentration ingredient in nitrite and therebyfacilitate movement of nitrite into the concrete.

Another compound suitable for use in the present invention would involvethe use of the source of aluminum not coming from cement. This wouldresult from the use of sodium aluminate NaAlO₄. This may be accomplishedby the following approaches.

 2NaAlO₄+3Ca(OH)₂+Ca(NO₂)₂→3CaO.Al₂O₃. Ca(NO₂)₂.nH₂O+2NaOH  (A)

wherein n=0 to 24 and preferably 0 to 12

or

2NaAl₂O₄+4Ca(OH)₂+2NaNO₂→3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O+4NaOH  (B)

wherein n=0 to 24 and preferably 0 to 12.

In certain embodiments of the invention, the aluminum constituent wasprovided in alumina form from calcium aluminate cement (CaO.Al₂O₃), ortricalcium aluminate cement (3CaO.Al₂O₃). Other sources may be employed.The alternate materials could be a source of alumina, aluminate oraluminum hydroxide having sufficient reactivity to form the desiredadmixture. For example, an alumina selected from the group consisting ofalpha alumina, flash calcined alumina, and transition aluminas may beemployed. Transition aluminas include gamma alumina, theta alumina, andkappa alumina, for example. Other calcium aluminates such as CaO.2Al₂O₃or CaO.6Al₂O₃ for example, could be employed. Suitable aluminates wouldinclude a source containing the AlO₂ ion and other alumina salts. Amongthe suitable aluminates are sodium aluminate and potassium aluminate.

Among other sources are organo-aluminates, such as sec-butoxide forexample. Other suitable sources are aluminum hydroxides such asnon-crystalline gels, forms of Al(OH)₃ such as gibbsite or bayerite,forms of AlOOH such as boehmite or diaspore and other hydrated aluminassuch as tohdite (5Al₂O₃.H₂O).

In another embodiment of the invention, a slurry or preformed panelcontaining a source of calcium such as Ca(OH)₂ and a source of aluminasuch as CaO.Al₂O₃ or 3CaO.Al₂O₃ which is either premixed with thecalcium source or applied separately, is applied over a concretestructure to sequester chloride ions from the concrete structure. Anexample of such a method of producing such an overlay is the followingreaction.

CaO.Al₂O₃+3Ca(OH)₂+nH₂O→3CaO.Al₂O₃Ca(OH)₂ −nH₂ O

wherein n=0 to 24 and preferably 12 to 18.

The reaction product will convert to 3CaO.Al₂O₃Ca(Cl)₂.nH₂O

wherein n=0 to 24 when it sequesters the chloride ion from the concretestructure.

It will be appreciated, therefore, that the present invention hasprovided an effective method and related compounds and structure forincorporating into concrete containing metal elements a class ofcompounds which will effectively resist undesired corrosion of themetallic compounds by both sequestration of chloride ions and provide acoating on the metallic elements, in some instances such as reactionsthat release nitrite. Other reactions, such as those which releasenitrate alone, occur without providing such a coating.

It will be appreciated that the compositions of the present inventionmay be combined with fresh concrete as defined herein in many ways. Forexample, the composition may be combined in solid form (a) with concretein a plastic state (b) with ready mix concrete at a job site (c) at thetime of batching or (d) inter-blended with mineral admixtures ofmaterials such as slag, fly ash, or silica fume, or (e) may beinterblended with cement, for example. It may also be combined in slurryform in a suitable liquid such as Ca(OH)₂ solution at the time ofbatching, for example. These approaches are all within the scope of thepresent invention.

In another embodiment of the invention, the chloride ion sequesteringcomponent or chloride ion sequestering and nitrite releasing compoundmay be created in situ. The compound 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O andsimilar compounds having the desired chloride ion sequestering orchloride ion sequestering and nitrite releasing capability may becreated in this manner.

One manner of effecting creation of the desired compound in situ wouldbe to add a solution containing NaAlO₄, Ca(NO₂)₂ and/or NaNO₂ to mixingwater to be employed to prepare fresh concrete. Alternatively, the addedmaterials could be mixed directly with the water. During cementhydration, Ca(OH)₂ would be produced and would react with the addedmaterials such as in reactions A and B. This results in in situ creationof a compound that both sequester chloride ion and releases nitrite.

As another approach, in lieu of relying on the concrete hydration toprovide the Ca(OH)₂, it may be admixed with one or more of NaAlO₄,Ca(NO₂)₂ and NaNO₂ and, be added to fresh concrete or to the mixingwater employed to prepare the fresh concrete.

Another approach to in situ creation would be to add calcium aluminatecement along with NaNO₂ or Ca(NO)₂ with or without Ca(OH)₂ to theconcrete making materials to create 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O in situwherein n=0 to 24 and preferably 12 to 18.

These general approaches may be employed in creating a slurry forremediation of concrete structures by mixing Ca(OH)₂ with NAlO₄,Ca(NO₂)₂ and/or NaNO₂ and providing the same on existing concrete. Thissame approach can be employed in creating pre-formed overlay panels foruse in remediation.

The hereinbefore described alternate sources of aluminum may be employedin this in situ embodiment along with NaNO₂ and/or Ca(NO₂)₂.

An alternate approach to the in situ embodiment would be to employnitrate salts such as NaNO₃ or Ca(NO₃)₂ which would produce a compoundthat sequestered chloride ions, but would not yield nitrites which wouldresult in an oxide protective layer on the metal elements.

In another embodiment of the invention employed to remediate a concretestructure, a solution containing a soluble source of alumina, such asNaAl₂O₄, for example, is combined within a solution, which may be anaqueous solution, with at least one material selected from the groupconsisting of Ca(NO₂)₂ and NaNO₂. This solution is introduced into thepores of the concrete structure to effect chlorine ion sequestrationwithin the concrete structure. The components would react with eachother and the Ca(OH)₂ contained within the concrete in order to producethe corrosion inhibiting compound. The nitrite which results from thereaction will serve to effect the creation of oxide protective layer onthe metal elements in the manner described hereinbefore. The solutionmay be introduced under pressure or by capillary suction after placingthe solution on the concrete surface, for example, thereby creating apressurized introduction into the pores. In the alternative, while notpreferred the solution may be allowed to infiltrate the pores under theinfluence of gravity.

It will fiber be appreciated that the present invention provides asystem for rehabilitation of an existing concrete structure through anoverlay which contains compounds which serve to sequester chloride ions.It may also establish an oxide barrier layer on metal structural membersassociated with the concrete structure.

Certain preferred compounds have been disclosed herein, along with theirmethod of use and resultant structure.

Whereas particular embodiments have been described herein for purposesof illustration, it will be evident to those skilled in the art thatnumerous variations of the details may be made without departing fromthe invention as defined in the appended claims.

What is claimed is:
 1. A method of resisting corrosion of metals in aconcrete structure comprising, creating a slurry containing at least onecompound capable of sequestering chloride ions selected from the groupconsisting of 3Me(II)O.R₂O₃.Me(II)(anion)₂ nH₂O where n=0 to 24 and3Me(II)O.R₂O₃.Me(II)(anion).nH₂O where n=0 to 18,  where Me(II) is oneor more divalent cations selected from the group consisting of Ca, Ba,Sr, Mn and Zn; R₂ is Al₂, Fe₂ or Cr₂; and  anion is NO₂, NO₃, CO₃, BO₄or OH, but when Me(II) is Ca, R₂ is not Al₂,  positioning said slurryadjacent to said concrete structure, and  sequestering chloride ions insaid compound.
 2. The method of claim 1 including creating an overlay onsaid concrete structure with said slurry and allowing said slurry toset.
 3. The method of claim 2 including securing said overlay to saidconcrete structure to permit chloride ion exchange therebetween.
 4. Themethod of claim 3 including applying a preformed panel over saidoverlay.
 5. The method of claim 4 including providing said preformedpanel with lower porosity than said slurry layer.
 6. The method of claim2 including employing in said slurry at least one material selected fromthe group consisting of NaAlO₄, Ca(NO₂)₂ and NaNO₂.
 7. The method ofclaim 2 including employing Ca(OH)₂ in said compound.
 8. The method ofclaim 2 including employing in said compound an aluminum constituentselected from the group consisting of alumina, aluminate and aluminahydroxide.
 9. The method of claim 8 including employing in said sourceof aluminum a material other than CaO.Al₂O₃ and 3CaO.Al₂O₃.
 10. Themethod of claim 2 including employing as said compound a compoundcapable of establishing a corrosion resistant oxide layer on embeddedmetal elements.
 11. The method of claim 2 including employing anitrite-containing compound as said compound.
 12. The method of claim 2including employing as said compound a compound selected from the groupconsisting of 3CaO.Fe₂O₃.Ca(NO₂)₂ .nH₂O; and 3CaO.Fe₂O₃.Ca(NO₃)₂ .nH₂O wherein n=0 to 24.